Tin plating baths



United States Patent US. Cl. 204-54 7 Claims ABSTRACT OF THE DISCLOSURE Electroplating bath for providing a bright tin deposit containing an anion, a non-ionic surfactant, tin ions and as a brightening agent, a carbonyl compound such as a heterocyclic or aromatic carbonyl compound with the carbonyl group directly attached to the ring.

This invention relates to improvements in electroplating baths for obtaining bright tin deposits.

Electroplating baths for the deposition of tin are well known. However, most of these baths suffer from the fact that the resultant tin deposits have a dull appearance which is unsuitable for many purposes. To brighten the tin deposits it was necessary to heat the deposit for a critical period of time and temperature.

To avoid such an aftertreatment, various additions to the tinplating baths have been proposed. Among such additions are the combination of two colloids of opposite electric charges such as a phenol resin and a beech wood extract and the reaction product of acetaldehyde and otoluidine. These baths, however, have not proved to be practical since the baths containing the phenol and beech wood extract are unstable and contaminate the work pieces. Also the baths containing the acetaldehyde-o-toluidine reaction products also have proved to be unsuitable because of the rapid resinification of the condensation product which reduces the life of the bath to a very short period of time.

A principal object then of our invention is to provide an improved electroplating bath for the deposition of bright tin deposits. This and other objects of our invention will be apparent from the description that follows.

- According to our invention we provide an acid electroplating bath containing bivalent tin ions, at least one anion selected from the group consisting of sulfate, benzenesulfonate and fluoborate ions, a reducing agent, a non-ionic surfactant and as a brightening agent a carbonyl compound selected from the group consisting of aromatic andv heterocyclic ring containing aldehydes wherein the carbonyl group is directly attached to an aromatic or aromatic ring and a, ,8 olefinically unsaturated carbonyl compounds.

The electroplating baths of our invention have the advantages of readily providing bright tin deposits even on work pieces having sharp edges or small apertures, allowing the electroplating to be carried out in a drum and permitting current densities of a factor of up to 1000.

Further, the baths of our invention have'the decided-- advantage of being particularly stable.

When the a, B olefinically unsaturated carbonyl compounds are employed, the bright tin deposits are immediately obtained. However, when the other types of carbonyl compounds are employed, the tin-plated objects, when removed from the bath, are coated with a thin brown-black layer which is readily removed by rinsing in a dilute alkali solution.

It is essential that the surfactant be a non-ionic surfactant as we have found that ionic surfactants do not 3,471,379 Patented Oct. 7, 1969 form a bright tin deposit over a wide range of current densities.

Further, it is essential that both the carbonyl compound and the surfactant be employed as the surfactant alone does not provide bright tin deposits and the carbonyl compounds alone provide bright tin deposits only in a very restricted range of current densities (about 5 to 20 A./cm. Thus the carbonyl compounds alone are not satisfactory for work pieces having sharp edges or plating carried out in a drum where the current density varies by a factor of or more.

The carbonyl compounds employed must be free of ionizable substituents and substituents reducible in the bath. Examples of such undesirable substituents are nitro, sulfonic acid, carboxylic acid, amino groups and substituted amino groups.

The at, 3 olefinically unsaturated carbonyl compound is a compound of the formula:

R2 R3 R4 wherein each of the symbols R R and R is a hydrogen atom, an aromatic, heterocyclic or aliphatic group or such a group wholly or partly hydrogenated, having, as the case may be, non-ionizable substituents or substituents not reducible in this medium, R is hydrogen, an alkyl group or an esterified carboxylic group or wherein the combination v I ll R13 is,.for example not in tautomeric relationship to form it. t,

or in other words has become of a purely unsaturated nature, it operates satisfactorily as a brightening agent in the sense of the invention.

The carbonyl compounds themselves or derivatives of the carbonyl compounds which are converted by hydrolysis in the bath into the carbonyl compounds may be employed.

Only small quantities of the carbonyl compounds (hereinafter called brightening compounds) are required. Thus quantities as small as about 25 mgs. per litre of bath liquid or even less are frequently sufficient. The upper limit is determined only by economic reasons and the solubility of the brightening agent. The concentration of the non-ionic surfactant may vary considerably usually from about 0.1 g. to 10 g. per litre of bath liquid.

Examples of non-ionic surfactants that may be employed are given in Detergents and Emulsifiers 1963 Annual. John W. McCutcheon, -Inc., Morristown, New

Example 1 An aqueous tin-plating bath of the following composition was prepared:

Stannous sulfate g 40 Sulfuric acid (d=1.84) g 120 Formalin g 5 Lissapol N (a non-ionic surfactant) g 1 A -dihydro-O-tolylaldehyde mg 30300 Water, to make 1 litre.

Several work pieces of the following description:

Elliptical loudspeaker baskets with a diameter of 7 inches made by deep-drawing of ordinary steel and presenting simultaneously a deep recess in the center, where the magnet is to be fixed, holes in the conical part of its surface and a prominent rim were tin-plated with the aid of this bath at a temperature of 20 C. and an average current density of 0.5 to 5 A./cm. measured externally. After 10 minutes the work pieces were removed from the bath and each was entirely covered with a bright layer of tin.

Several weeks later the bath was still capable of producing similar results and still uncontaminated by dirt.

By replacing the brightener of the bath with the indicated quantities of the following brightener similar results were obtained even though local current density variations of a factor of more than 100 were encountered.

Concentration per Brightener: litre of bath, mg. A -Dihydrobenzaldehyde 85 Cinnamic acid aldehyde 210 a-Ethyl cinnamic acid aldehyde 270 2,4-hexadienal 840 3-formyl,5,6-dihydro-2,6-dimethylpyrane 300 Benzalacetone 160 Benzalacetophenone 260 2-benzalcyclohexanone 160 Vinylphenylketone 280 p-Chlorobenzalacetone 160 Z-cinnamylthiophene 320 2-(w-acetyl)-vinylfurane 530 2-(w-benzoly)-vinylfurane 270 p-Cl-phenylstyrylketone 240 Isobutyl-styrylketone 200 w-Acetyl cinnamic acid ethyl ester 80 p-Toluylstyrylketone 160 When the following brighteners were employed the tinplated objects were dipped, after removal from the tinplating bath, in a solution of caustic soda lye in water 30 g./litre at a temperature of 80 C. for a period of 30 seconds after which a fine uniform tin gloss was visible:

Concentration per Brightener: litre of bath, mg. Benzaldehyde 3-ethoxy-4-hydroxybenzaldehyde 500 Salicylaldehyde 370 2,4-dimethoxybenzaldehyde 80 p-Chlorobenzaldehyde 32 p-Methoxybenzaldehyde 280 3,4-dihydroxybenzaldehyde 670 2,4,6-trihydroxybenzaldehyde 190 Thiophene-Z-aldehyde 1200 Indole-Ii-aldehyde 240 Similar results were obtained by the use of baths cont aining, in addition to the brightener, the following compositions:

Tin fluoroborate Sn(BF g 30 Fluoroboric acid g 200 Formalin 40% ml 10 60% solution of a non-ionic surface-active compound Lissapol N ml 2 Tin sulphate g 40 m-Benzene disulphonic acid g Formalin 40% ml 10 Lissapol N solution ml 1 What we claim is:

1. An acid electroplating bath for depositing bright deposits of tin, said bath comprising an aqueous solution containing tin ions, at least one anion selected from the group consisting of sulfate, benzenesulfonate and fluoroborate ions, a reducing agent, a non-ionic surfactant and as the sole brightening agent at least about 25 mg. per liter of a carbonyl compound selected from the group consisting of A -dihydro-o-tolylaldehyde, A -dihydrobenzaldehyde, 3-formyl, 5,6-dihydro-2,6-dimethylpyrane and 2-benzalcyclohexanone.

2. The electroplating bath of claim 1 wherein the brightening agent is A -dihydro-o-tolylaldehyde.

3. The electroplating bath of claim 1 wherein the brightening agent is A -dihydrobenzaldehyde.

4. The electroplating bath of claim 1 wherein the brightening agent is 3-formyl, 5,6-dihydro-2,6-dimethylpyrane.

5. The electroplating bath of claim 1 wherein the brightening agent is Z-benzalcyclohexanone.

6. The electroplating bath of claim 1 wherein the anions comprise mainly sulfate ions.

7. The electroplating bath of claim 1 wherein the concentration of the brightening agent lies in the range of about 25 to 300 mg. per litre of bath liquid.

References Cited UNITED STATES PATENTS 2,870,070 1/1959 Higgs et a1. 204-54 3,361,652 1/1968 Korpiun et a1. 204-54 FOREIGN PATENTS 299,792 7/1922 Germany. 842,898 7/1960 Great Britain.

HOWARD S. WILLIAMS, Primary Examiner G. L. KAPLAN, Assistant Examiner 

